Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4BC99C433F5 for ; Tue, 23 Nov 2021 00:38:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232184AbhKWAlO (ORCPT ); Mon, 22 Nov 2021 19:41:14 -0500 Received: from mail.kernel.org ([198.145.29.99]:48478 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232053AbhKWAke (ORCPT ); Mon, 22 Nov 2021 19:40:34 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id C703D60698; Tue, 23 Nov 2021 00:37:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1637627847; bh=icI5/M2hLsyGCbhSphBc5coM9+SCPQ4/0Gx+CvfZzhU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RBUK5rdkpegzgDD2OFNfoLYh6rHYgUdMWN019V51TelYBY3xJFtlgcWgX9S63/fPh /ezq2HRjyKYiwRHYopGYphRH5mEKIwVKRAqTbezGmcxT56GeJqXAObR19hAjJ+TXJs 18ba02urR+7wtGfEUT5q01ZyKmdW3tlS7V7VX73ZolbXoekGhPSZkrxrD7Zapzahcq q3im0kTGKNAZmtnYBGVWWXeT7nwgkULAS0KGy2XseoYnH2B7xQ6fLYqqSOVSv3VRm/ mR8AOHgYbhWZzuu3SllyQqmuRN2rYsDL3x8nmW7Em7mhtN4jV/d25XRmZcntI/cz6j rnTF6xPOh8nRQ== From: Frederic Weisbecker To: "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , Uladzislau Rezki , Neeraj Upadhyay , Boqun Feng , Josh Triplett , Joel Fernandes , rcu@vger.kernel.org Subject: [PATCH 5/6] rcu/nocb: Allow empty "rcu_nocbs" kernel parameter Date: Tue, 23 Nov 2021 01:37:07 +0100 Message-Id: <20211123003708.468409-6-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20211123003708.468409-1-frederic@kernel.org> References: <20211123003708.468409-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If a user wants to boot without any CPU in offloaded mode initially but with the possibility to offload them later using cpusets, provide a way to simply pass an empty "rcu_nocbs" kernel parameter which will enforce the creation of dormant nocb kthreads. Signed-off-by: Frederic Weisbecker Cc: Neeraj Upadhyay Cc: Boqun Feng Cc: Uladzislau Rezki Cc: Josh Triplett Cc: Joel Fernandes --- .../admin-guide/kernel-parameters.txt | 26 ++++++++++++------- kernel/rcu/tree_nocb.h | 10 ++++--- 2 files changed, 23 insertions(+), 13 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index cd860dc7c60b..6ff1a5f06383 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4351,20 +4351,28 @@ Disable the Correctable Errors Collector, see CONFIG_RAS_CEC help text. - rcu_nocbs= [KNL] - The argument is a cpu list, as described above. + rcu_nocbs[=cpu-list] + [KNL] The optional argument is a cpu list, + as described above. - In kernels built with CONFIG_RCU_NOCB_CPU=y, set - the specified list of CPUs to be no-callback CPUs. - Invocation of these CPUs' RCU callbacks will be - offloaded to "rcuox/N" kthreads created for that - purpose, where "x" is "p" for RCU-preempt, and - "s" for RCU-sched, and "N" is the CPU number. - This reduces OS jitter on the offloaded CPUs, + In kernels built with CONFIG_RCU_NOCB_CPU=y, enable the + no-callback CPU mode. Invocation of such CPUs' RCU + callbacks will be offloaded to "rcuox/N" kthreads + created for that purpose, where "x" is "p" for + RCU-preempt, and "s" for RCU-sched, and "N" is the CPU + number. This reduces OS jitter on the offloaded CPUs, which can be useful for HPC and real-time workloads. It can also improve energy efficiency for asymmetric multiprocessors. + If a cpulist is passed as an argument, the specified + list of CPUs is set to no-callback mode from boot. + + If otherwise the '=' sign and the cpulist arguments are + omitted, no CPU will be set to no-callback mode from + boot but cpuset will allow for toggling that mode at + runtime. + rcu_nocb_poll [KNL] Rather than requiring that offloaded CPUs (specified by rcu_nocbs= above) explicitly diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h index 9d37916278d4..d915780d40c8 100644 --- a/kernel/rcu/tree_nocb.h +++ b/kernel/rcu/tree_nocb.h @@ -66,14 +66,16 @@ static bool rcu_nocb_is_setup; static int __init rcu_nocb_setup(char *str) { alloc_bootmem_cpumask_var(&rcu_nocb_mask); - if (cpulist_parse(str, rcu_nocb_mask)) { - pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n"); - cpumask_setall(rcu_nocb_mask); + if (*str == '=') { + if (cpulist_parse(++str, rcu_nocb_mask)) { + pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n"); + cpumask_setall(rcu_nocb_mask); + } } rcu_nocb_is_setup = true; return 1; } -__setup("rcu_nocbs=", rcu_nocb_setup); +__setup("rcu_nocbs", rcu_nocb_setup); static int __init parse_rcu_nocb_poll(char *arg) { -- 2.25.1